does not consider friction. Assume that there is only the earth in the universe, and an object makes free fall from the direction of infinite earth. How fast can the final speed reach? Can it exceed the speed of light?
On the surface, the speed of an object will get faster and faster during the free fall, and the ultimate speed of the object should reach or even exceed the speed of light. The answer can be easily drawn using F=ma in Newton's mechanics.
But this way of thinking is only applicable to Newtonian classical mechanics, which is based on the absolute view of space-time and time, and is only applicable to the low-speed world.
And Einstein's theory of relativity tells us that time and space are not absolute. As the speed of objects gets faster and faster, the mass of objects will also increase. This is the qualitative effect. This shows that the mass m in F=ma is actually a variable. When m becomes larger and larger, more energy is needed to maintain the acceleration of the object. If it reaches the speed of light, infinite energy is needed. Obviously, this is impossible.
Therefore, no matter how far an object falls from, it will not reach the speed of light in the end, and it is even more impossible to exceed the speed of light. The free fall in the
question can easily make people feel illusion. In fact, free fall is equivalent to continuously applying force to the object, and using you as the gravity is also a kind of force.
In fact, the final speed of an object that falls freely from infinity cannot reach the speed of light, but will also be far smaller than the speed of light. The final speed is only 11.2 kilometers per second!
Is this speed very familiar?
Isn’t this the second Universe speed ? Is this a coincidence? Not, but inevitable.
can easily come up with this answer by using energy conservation. When an object falls freely from infinity, the whole process is the process of continuous conversion of gravity potential energy into kinetic energy. The result can be easily calculated using the formula mv^2/2=GMm/R.
During the free fall process, the object is indeed constantly accelerating by the earth's gravity, and the acceleration has always existed. However, the initial acceleration is infinitesimal, and it cannot reach 9.8 until the earth's acceleration reaches. The entire acceleration process can actually be regarded as a calculus process. Although the speed is constantly increasing, the final speed is not infinite, but a fixed value.
In fact, the process of free falling of objects is easier to understand.
Earth's escape speed is 11.2 kilometers per second, which means that an object can escape the earth's gravity and fly out of the earth at a speed of 11.2 kilometers per second. In fact, it can be understood in this way that this object did not escape the gravity of the earth. It just flew to an infinite place and then returned to the earth.
In this way, if this object falls to the earth from an infinite distance, its final speed will of course be 11.2 kilometers per second!
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